An inverter of a large capacitance used in system interconnection had the problem that the switching loss is so great that the operating frequency cannot be increased. In this context, application of soft-switching is effective.
Various soft-switching inverter circuits have been proposed. For example, the soft-switching inverter circuit disclosed in Non-Patent Document 1 (Shinsuke Kadoi, Hirotake Nakaji, Yushi Miura, Toshifumi Ise, Yasuhiko Hosokawa, “A Soft-Switching Inverter Circuit without Active Switches in Auxiliary Circuits”, National Conference of the Institute of Electrical Engineers of Japan, 2011, Vo. 14, pp. 113-114) is characterized in that an active element is not employed in auxiliary circuits, general PWM (Pulse Width Modulation) control is allowed, and the maximum voltage of the main element can be suppressed by the passive clamp circuit.